By the time of their divorce they were worth $1.85 million, taking the total value of their superannuation fund to $3.4 million.

He took a calculated risk with the parties' money, which fortunately proved correct

Because of the husband's "skill in selecting and pursuing the investment", the judge awarded him two thirds of the fund, or $1 million more than the wife.

But the full Family Court of Australia has overturned that decision, finding the trial judge may have given "unacceptable weight" to the husband's "special skills", in a case which could have major ramifications for divorces in the big end of town.

Advertisement

The controversial "special contribution" doctrine has previously allowed one spouse to lay claim to a significant portion of a couple's assets if they showed exceptional skill or talent in building the fortune.

But the December 18 judgement, published online this week, in the case known as Kane & Kane has significantly challenged that principle.

The couple, with four children separated in 2009 after almost 30 years of marriage. Their assets totalled $4.2 million, but it was the superannuation fund that caused a legal battle. All other assets - totalling less than $800,000 - were divided equally.

Family Court deputy chief justice John Faulks said the original judge's disproportionate division of the property "could not be justified".

"It is difficult to correlate effort or skill (even if special) with result," he wrote. "Frequently, the financial result of a contribution (whether by physical or intellectual labour or imagination foresight and perspicacity) will be influenced by external factors beyond the control of the party contributing."

Furthermore, he noted that Mr Kane did not have any professional qualifications or special knowledge of the business in which he invested. And that he "took a calculated risk with the parties' money, which fortunately proved correct".

Family law expert Glenn Thompson said the decision was "very significant" and meant judges were no longer bound by precedent.

"It's saying there's nothing in the Family Law Act that one contribution is special as opposed to another and should be treated higher than any other contribution," he said. "You've got to weigh up all the different types of contributions, be it the homemaker and parent, be it the breadwinner, be it inheritance, be it physical labour."

One of the key criticisms of the doctrine has been that it discriminates against women and undervalues the role of the mother.

"[The Kane & Kane decision] is saying that the role of the homemaker and parent is a significant role that shouldn't be undervalued," Mr Thompson, who is a member of the Family Issues Committee of the Law Society of NSW, said.

"It should lead to a more equal result in a lot of the bigger money cases because if the assets were all built up whilst the parties were together then they're going to be an equal contribution."

The Kane & Kane settlement has been called back for rehearing before a new judge.